1) Field
This embodiment relates to a semiconductor light emitting device having a ridge structure formed on a GaAs substrate such as a semiconductor light emitting device which operates, for example, as a light source for optical fiber communications and a fabrication method for the semiconductor light emitting device.
2) Description of the Related Art
In recent years, development of lasers for optical fiber communications whose operation wavelength is within a wavelength band longer than 1 μm and in which a GaAs substrate is used such as quantum dot lasers, GaInNAs lasers and so forth is advancing.
As one of such lasers for optical fiber communications as just described, a semiconductor laser having a ridge structure including an AlGaAs cladding layer has been proposed.
In order to allow a semiconductor laser having a ridge structure including an AlGaAs cladding layer to operate in a single transverse mode, it is necessary to accurately control the width and the height of the ridge structure.
Usually, the ridge structure is formed by etching, and the width thereof can be controlled with the width of an etching mask. Further, since the height of the ridge structure depends upon the depth of etching, the height can be controlled by such a method as control of etching time or insertion of an etching stop layer.
Particularly, control of the etching depth is significant and, if the etching depth has a variation by approximately 0.1 μm from a designed value, then the cutoff waveguide width of a higher-order transverse mode of the ridge waveguide varies by approximately ±0.5 μm.
Therefore, as a high accuracy etching method for a semiconductor laser having a GaAs/AlGaAs-related ridge structure, a method is known wherein an AlGaAs layer having a high Al composition ratio (for example, the Al composition ratio is approximately 0.5) is used as a cladding layer and a GaAs layer is used as an etching stop layer, and the etching depth is controlled with an AlGaAs/GaAs interface using fluoric acid capable of selectively etching an AlGaAs cladding layer as etchant (for example, refer to Japanese Patent Laid-Open No. Hei 5-304336).